These studies are designed to elucidate the pathogenesis of Multiple Sclerosis. Our approach to this problem is based largely on the two current hypotheses regarding pathogenesis, i.e., an autoimmune and a viral etiology. Our studies based upon the first hypothesis deal largely with the animal model, allergic encephalomyelitis (EAE). These studies are designed to reveal basic immunological mechanisms underlying the production and suppression of the experimental disease. In particular, we are interested in defining those determinants of the myelin basic protein molecule which are responsible for disease induction, cell-mediated immunity and antibody formation. The particular animal model we have chosen is EAE in the Lewis rat produced by guinea pig basic protein and a fragment of this protein (residues 44-89). The studies based upon the viral hypothesis consist of two aspects. The first of these is the attempt to culture virus from the brains of patients who die with multiple sclerosis and the second is an attempt to relate the measles virus to the disease. The latter study consists primarily of an attempt to culture the virus in sufficient quantities to obtain purified, antigenic, viral components. BIBLIOGRAPHIC REFERENCES: McFarlin, D.E., Hsu, C.-L.S., Slemenda, S.B., Chou, F.C.-H., and Kibler, R.F., The immune response against myelin basic protein in two strains of rat with different genetic capacity to develop experimental allergic encephalomyelitis. J. Exp. Med., 141:72-81, 1975. McFarlin, D.E., Hsu, C.-L.S., Slemenda, S.B., Chou, C.-H., Jen, and Kibler, R.F. The immune response against an encephalitogenic fragment of guinea pig basic protein in the Lewis and Brown Norway Strains of Rat. J. Immunol., 115:1456-1457, 1975.